Thermal conversion of hydrocarbons



Aug. 17, 1937. c. c. TowNE THERMAL CONVERSION OF HYDROCARBONS Filed March 28, 19153 Wi/FAES Cf 70W/Vf' /N VEA/TOR /f/ A TTORNE Y /f/f A Patented Aug. 17,J 1937 UNITED STATES PATENT oFr-ICE THERMAL CONVERSION oF cAmsoNs HYDRO- Application March 28,

4 Claims.

This invention relates to the thermal conversion of hydrocarbons and more particularly to the cracking of low boiling hydrocarbons, such as naphtha and natural gas hydrocarbons, to

5 produce valuable products siutable for the manufacture of a motor fuel or gasoline of high antiknock value. The invention still more particularly has to do with a process involving both the pyrolysis of normally gaseous hydrocarbons and the reforming of naphtha.

The conversion of hydrocarbon gases, such as natural or refinery gases `or fractions thereof like ethane, propane, butane or their mixtures, into aromatic liquids typified by benzene, tolu- '15 ene, xylene; and the reforming of naphtha of relatively low anti-knock value, such as straight run naphtha or fractions thereof, to increase the anti-knock value; are processes known in the art. I have now found that the above processes, which heretofore had been proposed to be operated separately, may be advantageously carried The hydrocarbon gases to be cracked are fedthrough the pipe 5to heater coil 6 located within a suitable furnace setting 1. In the heater the gases are rapidly raised to a conversion temperature which will vary somewhat, depending on the charge. Suitable temperatures are about 1650 F. for ethane, 1475? F. for propane, 1385" F. for btanefetc. For a mixture thereof as, for example, natural gas or certain fractions of natural gas, an average temperature of around 1500 F. would be most suitable but in any event, a temperature range betweenI 12501750 F. should be used. The time for raising the gases to the desired temperature should ordinarily not require more than 0.001 minute, and usually considerably less. The hot gases, at a conversion temperature, are transferred through line 8 controlled by a valve 9 to a reaction vessel III. In the reaction vessel, time is allowed to effect conversion of cracked products into aromatics. The reaction is exothermic and a cooling medium, preferably a portion of the charge, may be introduced into the products entering the reaction vessel to avoid excessive rise in temperature. The time required for reaction in the vessel Ill for an optimum yield of aromatics is usually not over 0.1 minute, and preferably consid- .55 erably less, .Atmospheric pressure or there- 1933, Serial No. 663,135

abouts is preferably maintained on the heater coil 6 and reaction vessel I0.

The reaction in the vessel I0 should be substantially complete or complete to a point to produce a maximum yield of aromatics. The products are delivered through a pipe I5 ,controlledby a valve I6 to a pump or compressor Il. It is often advantageous to-cool the products issuing from the vessel I0 and such cooling might be done by a suitable cooler installed in the line I5, or a portion or all of the naphtha from the line I8, referred to hereinafter, may be charged through the pipe I9 controlled by a valve 20 into the hot gases in the pipe I5. The reduction of the temperature of the hot cracked products from vessel I0 may be in the nature of shock cooling and has the effect of reducing the temperature below that at which further reactions affecting the yield of aromatics occur. The heat is absorbed by the naphtha and causes reforming thereof, as explained more fully hereinafter. The hotgases are compressed by the compressor I1 to a pressure approximately that maintained in the soaking drum 25 to which they are transferred from the compressor through a line 2| controlled by valve 22.

Attention is now directed to the important feature of the invention of introducing naphtha into the products of reaction in the soaking drum 25. The naphtha is introduced, as shown in the drawing, through the line I9, referred to heretofore, or through the line 30 controlled by valve 3l. In either case the naphtha is contacted with the hot gaseous reaction products from the reaction vessel I0. Instead of mixing the naphtha with the products in the transfer line I5 or 2|, it is contemplated that `the naphtha may be introduced directly' intothe soaking drum, or that a mixing chamber preceding the soaking drum be provided in which the gaseous reaction products and naphtha are thoroughly commingled and the resultant mixture transferred to the soaking drum.

The naphtha mixed with the gas pyrolysis products may be all or in part raw naphtha, of low anti-knock value and suitable for reforming, introduced through pipe 32 controlled by valve 33. However, I prefer to at least preheat the naphtha 'suiliciently to effect vaporization thereof, in which case the naphtha is charged through line 34 into the heating coil 35 located within the furnace 36. The preheated naphtha is then transferred through line I8 and eventually mixed with the hot cracked gases. The naphtha` absorbs heat from the cracked gases thereby cooling the gases and heating the naphtha to reforming temperatures.

In the soaking drum a temperature of about 800-1050 F. and preferably about 950 F..is 5 maintained. The pressure may be about 'Z50-3000 lbs., and preferably around 2000 lbs. per sq. in. The reaction in the soaking drum produces a reforming of the naphtha whereby constituents of low anti-knock value are transformed into products of increased anti-knock value. Also, reactions between the cracked products from the gas pyrolysis and the naphtha reforming operations, favorable for the production of gasoline constituents, may take place in the soaking drum. y

According to o ne modification of the invention, I may heat any or all of the naphtha to reforming temperatures in the coil 35 and eifect substantial or complete reforming therein. The reformed or partially reformed naphtha is then mixed, as explained heretofore, with the hot products of the gas pyrolysis operation. The mixture of cracked products from both sources is subjected to further reaction in the soaking drum 25. The reactions taking place in the soaking drum are favorable for the production of an increased yield of products suitable for the manufacture of high anti-knock motor fuel and the amount of tar and coke formation may be substantially reduced.

'I'he products from the soaking drum are transferred through line 40 controlled by valve 4| to separator 42 wherein the temperature becomes substantially reduced and carbonaceous material and high boiling, tars are separated. 'I'he products separated in the chamber 42 may be withi drawn through the line 43 controlled by valve 44.

Suitable cooling may be provided in the separator 42, if desired, such as a cooling coil or direct contact with a cooling medium, such as heavy hydrocarbon oil like fuel oil, crude petroleum, etc. The vapors of gasoline and uncondensed aromatics from the tar separator are transferred through line 45 controlled by valve 46 to a fractionator 50. In the fractionator, products of substantially higher boiling range than commercial gasoline are condensed and separated as a reflux condensate which may be withdrawn through line 5i controlled by valve 52. 'I'he reflux usually constitutes a suitable cracking stock and may be recycled,` if desired, all or in part to the naphtha reforming coil 35 or through the naphtha line 32.

The uncondensed vapors containing motor fuel 55 hydrocarbons are conducted through line 55 controlled/iby valve 56 to condenser 51. The major portion of the liqueflable constituents are liquefied in the condenser and drain into accumulator 58 from which gasoline containing aromatics may be.. discharged through the pipe 59 controlled by valve 60. 'I'he gases and uncondensed vapors entering the accumulator may be discharged through conduit 6I controlled by valve 62 into the absorber or scrubber 65 wherein the gases 5 are contacted with an absorption medium, such as mineral seal or other absorbent oil introduced from pipe 66. The rich absorbent oil is discharged from the scrubber through pipe 61 which conducts the mixture to a still or other suitable 10 means for recovering-the absorbed constituents.

The light products recovered from the absorber may be combined with the gasoline-like products in the accumulator to produce a suitable high anti-knock value motor fuel. Thexed gases 75 are removed from the scrubber through the pipe 68 controlled by the valve 69 and disposed of as desired, but I prefer to return them all or in part to the pipe 5 leading to the primary cracking coil 6.

'I'he pressure on those parts of the apparatus succeeding the soaking drum 25 may be regulated by the valves 4|, 46, 56, 62 and 69. A satisfactory pressure may be about 500-1000 lbs. on the separator and fractionator and about 100-300 lbs. on the scrubber.

As an example of the operation of the invention, a fraction from a stabilizer in the natural gas industry and consisting largely of propane is heated to about 14'75" F. in the heater 6. About 0.002 minute is required to obtain this temperature and the products are then transferred to the reaction vessel l0 where they are allowed to react for about 0.05 of a minute. 'I'he products are cooled to approximately 1200 F. by heat exchange with naphtha. The products are then compressed to about 1500 lbs. per sq. in. 'I'he final temperature of the compressed gases is around 1300 F. due to a slight rise in temperature during compression. For every 1000 cubic feet of gas charged to the heater 6 I prefer to charge about 100 gallons of the heavier ends of a naphtha boiling about 200-450 F. 'Ihe naphtha is preheated to around 500 F. and mixed withthe hot gases from the gas pyrolysis process and the mixture subjected to reaction in the soaking drum. The

temperature in the soaking drum is around 950' F. and the pressure about 1500 lbs. per sq. in. A pressure of about 1000 lbs. is maintained on the tar separator and fractionator. The temperature of the tar separator is about ri00800 F.

and the temperature of the fractionator about 500-600 F. at the bottom and around 410-425 F. at the top. A motor fuel of gasoline boiling range is recovered in the accumulator 56. l About 2-7 gallons more of light motor fuel is recovered in the scrubber. The combined motor Vfuel cuts recovered from the accumulator and the scrubber amount to approximately 85% of the naphtha charged and have an octane number 'of about 80.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be" made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the ap- Dended claims.

I claim: l

1. A process for the combined pyrolysis of hydrocarbon gases and for the reforming of naphtha which comprises subjecting normally gaseous hydrocarbons free of products of combustion to a pyrolysis operation at elevated temperature and maintaining said gases at elevated temperature to produce a substantial amount of aromatic compounds, separately subjecting a naphtha of relatively low anti-knock value to a reforming operation to increase the anti-knock value thereof, mixing the products from the gas pyrolysis operation after said substantial amount of aromatic compounds has been formed with the product from the naphtha reforming operation, subjecting the resultant mixture to a soaking treatment, and separating a high anti-knock motor fuel from the resulting products.

2. In the combined pyrolysis of hydrocarbon gases and reforming of petroleum naphtha, the process that comprises subjecting gaseous hydrocarbons free of products of combustion to a conversion operation wherein normally gaseous hydrocarbons are subjected to elevated temperature and maintained at elevated temperature to convert them into a substantial amount of products within the gasoline boiling range, separately subjecting a petroleum naphtha to a heat treatment wherein constituents of the naphtha are transformed into products of increased anti-knock value, mixing the products from the gas pyrolysis after said products within the gasoline boiling range have been formed with the products from the naphtha reforming operation and subjecting the resulting mixture to a soaking operation at approximately the temperatures of the naphtha reforming operation.

3. In the combined pyrolysis of hydrocarbon gases and reforming of petroleum naphtha, the process that comprises subjecting gaseous hydrocarbons free of products of combustion to a conversion operation wherein normally gaseous hydrocarbons are subjected to elevated temperature and maintained at elevated temperature to convert them into a substantial amount of products within the gasoline boiling range, separately subjecting a petroleum naphtha to a heat treatment wherein constituents of the naphtha are in part transformed into products of increased antiknock value, admixing the products from the gas pyrolysis after said products within the gasoline boiling range have been formed with the products from the partial reforming operation and subjecting them to conditions of pressure and temperature effective to promote further conversion of naphtha constituents, withdrawing the resultant vaporous products and fractionating them to recover a motor fuel fraction of high antiknock value.

4. A process for the combined pyrolysis of hydrocarbon gases and for the reforming of naphtha which comprises subjecting normally gaseous hydrocarbons free of products of combustion to elevated temperature, reacting said gases at elevated temperature in a reaction zone for a suicient period of time to effect conversion of normally gaseous hydrocarbons into a substantial amount of products within the gasoline boiling range', withdrawing said converted products from the reaction zone and cooling them, separately subjecting naphtha to heat treatment to effect reformation of constituents thereof, mixing the cooled products of the gas conversion after said products within the gasoline boiling range have been formed with the products from the naphtha'reforming operation, subjecting the resulting mixture to soaking at elevated temperature and recovering a high anti-knock motor fuel from the resulting products.

CHARLES C. TOW'NE. 

